1. Field of the Invention
This invention relates to an injection molding process and more particularly, this invention relates to a co-injection molding process for molding relatively complex and large shapes by a process that results in molded products having a lighter weight then heretofore produced, and molded product parts that are produced at a lower overall cost.
2. Description of the Prior Art
The co-injection molding process in comparison to the standard injection molding process offers the potential to reduce cost and improve quality of the part by using an overall simpler process for injection molding. At the same time the co-injection molding process permits one to produce relatively large and complex parts.
In the co-injection molding process a first material (such as first resin) is injected into a mold cavity, followed by, or simultaneously with, the injection with one or more other materials (e.g. a second resin) into the same cavity. This method typically results in the article having multiple layers across its cross-section and generally a greater number of layers than material types as in the case where sequential injection of the material is used.
The injection molding art includes the disclosure of many different apparatus and processes for forming molded articles from multiple resins by co-injection molding. For example, both U.S. Pat. Nos. 5,028,226 and 4,717,524 show simultaneous and sequential co-injection molding apparatus and processes respectively. Both patents show one nozzle dedicated to a mold cavity wherein the mold cavity is completely filled for molding purposes by injecting a multitude of resins through a single gate orifice.
An alternative co-injection molding process is shown in U.S. Pat. No. 4,803,031, where molded articles are formed by injecting one resin into a cavity and filling the cavity space, and thereafter enlarging the cavity and filling the additional space with a second resin. The result of such a technique is two distinct molded areas, each comprising a different resin type.
U.S. Pat. No. 3,873,656 illustrates a co-injection molding apparatus wherein a multitude of plastics are injected into a mold cavity through a number of different gates. The timing of the opening and closing of the gates dictates the amount and extent of the resin types which form the molded article. The design is basically suitable for molding very large plastic articles, wherein a multitude of gates can be used.
U.S. Pat. No. 5,173,736 describes a fuser apparatus for a printing machine wherein the fuser apparatus, i.e. a heated fuser roll has endcaps fitted to the opposing ends of the roll. The endcaps are disclosed as being made of aluminum (e.g. the roller member and the endcaps are a single piece).
U.S. Pat. No. 4,538,052 discloses a "prior art" fuser roller and an improvement thereof. The fuser roller comprises an aluminum roller member with stainless steel endcaps. Preferably the endcaps are fitted to the aluminum roller member under pressure using frictional heat.
U.S. Pat. No. 3,437,032 discloses a fuser roll which is similar to the above-mentioned prior art fuser roll in that stainless steel endcaps are shown secured to the ends of a nickel-plated copper tube. To avoid the technical difficulties in securing stainless steel to another metal, as well as the relatively high manufacturing costs associated with such a securing technique, U.S. Pat. No. 4,538,052 discloses an improved fuser roller in which a pair of bearings, having an outer portion made of heat-resistant resin, are fitted into end portions of the aluminum cylinder under pressure to support the cylinder so that the outer portion and cylinder turn as one unit. The heat-resistant resins are more economical than the metal members, and the outer portions of the roller can easily be fit into both end portions of the aluminum cylinder by merely pressing them against both end portions of the cylinder.
U.S. Pat. No. 5,980,245 discloses an endcap for a heated fuser roller which substantially reduces heat loss through the ends of the roller and is of sufficient strength and durability to transmit rotation to the rollers during extensive use. The endcap is molded from thermoplastic polymide filled with 20 to 50 weight percent glass fiber.
U.S. Pat. 5,649,891, discloses a composite endcap for a heated fuser roller which comprises a metal portion and a polymer portion. The endcaps are described as endcaps that substantially reduce heat loss through the end of the roller, and are of sufficient strength to support and transmit rotation to the roller.
In view of the current state of the prior art technology, there exists a need to have an injection molding process which can yield large and relatively complex parts at a significantly less expensive cost level than heretofore possible combined with producing an overall lighter weight part. A commercial part such as an end cap for a xerographic fuser roll fits into this category due to the high feedstock costs for metal injection molding such a part. In addition, most commercial parts made by injection molding processes are of a small size to minimize material usage.
Accordingly it is a primary advantage of this invention to provide a new and improved process for producing complex and large commercial parts which avoids all of the disadvantages outlined above. Other advantages of this invention are to employ a co-injection molding process for producing complex, large, lightweight and less expensive than heretofore possible commercial parts; and also to employ a co-injection molding process to produce end caps that can be employed in a xerographic fuser roll assembly. Additional advantages of the invention will be set forth in part in the description which follows, and some will be obvious from the description, or may be learned by practice of the invention in accordance with various features and combinations as particularly pointed out in the appended claims.